In conventional hard disks having a rotating magnetic medium, there is only one magnetic layer to record data. As such, the servo pattern information is recorded in servo wedges. This is illustrated in FIG. 1. FIG. 2A is a schematic showing the layout of servo information and data. FIGS. 2B, 2C and 2D are schematics showing a more detailed layout of servo information. As illustrated in FIG. 1 and FIGS. 2A-D, servo pattern information is stored between data areas for user data.
FIG. 3 a schematic showing a servo control system accessing a conventional data arrangement system in a conventional magnetic medium. The servo pattern information is accessed by the read/write head. The data is the transmitted to the preamplifier 302 and then to the auto gain control (AGC) 304. The analog signals are digitized by the analog to digital converter (ADC) 306. The digital signal is then transmitted to a position error signal (PES) demodulator 308 and compared with a reference signal to generate a position error signal. The ADC and PES demodulator are driven by timing recovery circuit 310. The position error signal (PES) provides an indication of whether the read/write head is off-track from the centre of the targeted track. The position error signal (PES) is provided to a controller 312 which then controls actuator driver 314 to position the read/write head on track.
For a servo control system such as that shown in FIG. 3, the position of the read/write head to be moved is obtained from the servo information stored in servo wedges. The sampling frequency of the servo control system is thus limited by the number of servo wedges in one revolution, and the rotating speed of disk. To improve the servo performance, such as tracking accuracy for high track density drive, a higher sampling rate is needed, which in turn requires more servo wedges to be placed in the magnetic layer. However, this will cause less data sector to be available for recording the user data. This is undesirable.